ALLEN MILLYARD
It’s a case of brakes and wheels to get this beauty rolling and stopping right.
This month Allen sorts brakes and wheels on the 374.
After last month’s successful test run of my 374cc six-cylinder engine I’m now really excited to be making a start on the rest of the bike. My aim was to make a six-cylinder RC174 tribute that has the right feel, correct scale, and most important to me the right sound, but not necessarily an exact replica.
I have named my bike the RC374 due to its actual engine capacity of 374cc. The original Honda RC174 was in fact 297cc. With this in mind I needed some nice clear photos of the original RC174 to follow while I was making parts, so as to capture the fine details. My birthday was approaching so I hinted to my wife Tracey that I needed a reference book on the Honda RC174 and gave her a link to one I had seen online. It was a guidebook for model makers, but to me this was perfect because it featured actual close up photographs of an authentic Honda RC174. When I make a bike from scratch I like to make parts in a certain order, engine first, then wheels followed by forks, swingarm and the frame last. This way I have all the main components to fit into a frame jig while I build the frame. I had recently bought a 1966 Honda CB77 bare rolling chassis thinking that I could use some of the parts. The wheels had twin-leading drum brakes, which looked like they may be usable, also the forks look similar, and with a bit of work could be made to look like original RC174 forks. The first thing I did was to strip the rolling chassis, making a pile of parts that were potentially usable. The wheels were rusty so I cut the spokes to remove the hubs. The rear hub was basically okay with one exception, it had to be flipped around so that the chain drive was on the left which involved a bit of modification to the brake plate; more on that later.
The Honda RC174 is fitted with a double-sided four leading shoe (4LS) drum front brake, which was a prominent feature on the original bike. The CB77 front hub was only a single-sided twin leading shoe drum so was no good to use in standard form. I did have a quick look online and found several companies making 4LS front hubs but they are expensive and didn’t really match up with the original look I was aiming for. I had already decided that I wanted to make as much as possible myself by hand from raw materials so I thought why not make the front hub from scratch as well? I was going to modify and use the CB77 forks and yokes so I had the dimension between the axle mounting points that determined the width of my hub. I then realised that I had to make a twin-sided four leading brake to fit in the same place as the standard twin leading brake, ‘this is going to be interesting,’ I thought to myself. I made a basic layout sketch to see how much space I had to work with, adding up known dimensions like the
width of CB77 brake shoes, wheel bearings and brake plates then subtracting the width of the speedo drive because this wouldn’t be needed and then taking the final figure away from the dimension between the forks. I was pleased to find there was 12mm left over which I would need for the internal central spokes. The next thing I did was to buy some cast iron to machine the internal braking surface rings. I needed 200mm internal bore to suit the Honda CB77 brake shoes and I thought it would be cheaper if I bought a pair of car drums to make them from. I had a look online again and found and bought a pair of 1970s Vauxhall Chevette brake drums that were 200mm internal diameter. ‘Perfect’, I thought; the car drums were made from the correct grade of cast iron and would require the minimum amount of machining. I set them up on my lathe and parted off a portion from each drum to machine into the rings for my new hub. I then ordered a solid billet of 6082T6 aluminium alloy to machine the main body of the hub on my lathe. This was a really interesting job to do, working to a few basic dimensions with my model maker’s guidebook for reference. Once the lathe work was complete, I set up the part finished hub up onto my milling machine to machine the internal spokes and drill the 36 spoke holes. The hub was then heated to 150°C in the oven, first making sure that Tracey wasn’t planning to use it for the next hour or so! Once the hub was heated through I quickly measured the internal diameters, which had now expanded and then finished machining the iron rings 0.05mm larger on the outside diameter to provide a tight interference fit. The rings were then pressed into each side of the hub on my hydraulic press. When the hub cooled the rings were held securely in place. As an additional precaution I also pinned the rings in three places. I then pressed one wheel bearing and made the internal spacer tube to suit and pressed in the second bearing. Next up was the brake plates; these were modified from original Honda CB77 brake plates to look similar to the RC174 brake plates by fabricating and welding on air scoops, and modifying the brake linkages on the left-hand brake plate. The righthand brake plate was originally on the left-hand side and needed more work to swap the positions of the pivots and cams to make the brake twin leading. If I had left the pivots where they were the right side brake would be twin trailing and not very effective. I had to do this modification on the rear brake plate as well due to the Honda CB77 having its chain on the right-hand side as I will be fitting it flipped over so that the chain is on the left. The last job I had to do to both front brake plates was relocate the anchorage point. I made a pair of triangle plates and welded one to each fork leg then made an aluminium boss to weld on to each brake plate that lined up with the triangle anchor point on each fork leg. After a trial fit to confirm all parts fitted and the hub rotated freely I was ready to complete the build of the wheels. I bought a pair of 18in flanged aluminium rims that are similar to the original Honda rims. The rear spokes were standard CB77 and laced in a three-cross pattern (this is the term given to how many spokes a single spoke will cross between the hub and rim) but the front spoke length were unique to my wheel and needed to be specially ordered. I used an online spoke length calculator to determine the required spoke length after measuring a few critical dimensions from the hub and rim and specifying the two-cross spoke pattern as used on the Honda RC174 front wheel. I then ordered the new spokes and a week later when they arrived I built up the wheels and fitted the period-looking tyres. Superb!